The double-wishbone suspension can also be referred to as "double A-arms," though the arms themselves can be A-shaped, L-shaped, or even a single bar linkage. A single wishbone or a-arm can also be used in various other suspension types, such as macpherson strut and chaman strut. The upper arm is usually shorter to induce negative camber as the suspension jounces (rises), and often this arrangement is titled an "SLA" or short long arms suspension. When the vehicle is in a turn, body roll results in positive camber gain on the lightly loaded inside wheel, while the heavily loaded outer wheel gains negative camber.
Between the outboard end of the arms is a knuckle with a spindle, hub, or upright which carries the wheel bearing and wheel.
To resist fore-aft loads such as acceleration and braking, the arms require two bushings or ball joints at the body.
At the knuckle end, single ball joints are typically used, in which case the steering loads have to be taken via a steering arm, and the wishbones look A- or L-shaped. An L-shaped arm is generally preferred on passenger vehicles because it allows a better compromise of handling and comfort to be tuned in. The bushing inline with the wheel can be kept relatively stiff to effectively handle cornering loads while the off-line joint can be softer to allow the wheel to recess under fore-aft impact loads. For a rear suspension, a pair of joints can be used at both ends of the arm, making them more H-shaped in plan view. Alternatively, a fixed-length driveshaft can perform the function of a wishbone as long as the shape of the other wishbone provides control of the upright. This arrangement has been successfully used in the jagure IRS. In elevation view, the suspension is a 4-bar link, and it is easy to work out the camber gain and other parameters for a given set of bushing or ball-joint locations. The various bushings or ball joints do not have to be on horizontal axes, parallel to the vehicle centre line. If they are set at an angle, then antidive and antisquat geometry can be dialed in.
In many racing cars, the springs and dampers are relocated inside the bodywork. The suspension uses a bellcrank to transfer the forces at the knuckle end of the suspension to the internal spring and damper. This is then known as a "push rod" if bump travel "pushes" on the rod (and subsequently the rod must be joined to the bottom of the upright and angled upward). As the wheel rises, the push rod compresses the internal spring via a pivot or pivoting system. The opposite arrangement, a "pull rod," will pull on the rod during bump travel, and the rod must be attached to the top of the upright, angled downward. Locating the spring and damber inboard increases the total mass of the suspension, but reduces the unspring mass, and also allows the designer to make the suspension more aerodynamic.
